The present invention relates generally to polymeric materials that display periodic ordering, and more particularly to a polymeric article defining an optical band gap material.
Photonic band gap materials, that is, materials that can control the propagation of electromagnetic radiation by creating periodic dielectric structures, have been the subject of vigorous research in recent years. A photonic band gap material is one that prohibits the propagation of electromagnetic radiation within a specified frequency range (band) in certain directions. That is, band gap materials prevent light from propagating in certain directions with specified energies. This phenomenon can be thought of as the complete reflection of electromagnetic radiation of a particular frequency directed at the material in at least one direction because of the particular structural arrangement of separate domains of the material, and refractive indices of those domains. The structural arrangement and refractive indices of separate domains that make up these materials form photonic band gaps that inhibit the propagation of light centered around a particular frequency. (Joannopoulos, et al., xe2x80x9cPhotonic Crystals, Molding the Flow of Lightxe2x80x9d, Princeton University Press, Princeton, N.J. 1995). One-dimensional photonic band gap materials include structural and refractive periodicity in one direction, two-dimensional photonic band gap materials include periodicity in two directions, and three-dimensional photonic band gap materials include periodicity in three directions.
Ho, et al., xe2x80x9cExistence of Photonic Gaps in Periodic Dielectric Structuresxe2x80x9d, Phys. Rev. Lett., 65, 3152 (1990) correctly predicted that a properly-arranged, three-dimensional photonic band gap material would include a complete band gap, that is, that the material would reflect light of any polarization incident at any angle at a particular frequency. If one or more defects are created in such a material, the material can serve a variety of useful purposes. Point defects could define low loss optical resonance cavities, planar defects could define narrow-band filters, and pathways within three-dimensional photonic band gap materials could define lossless waveguides capable of guiding light around sharp corners, crucial to the creation of proposed optical computers. Totally-reflective UV or laser shields, and countless other commercial applications would benefit from relatively simple and reliable techniques for forming these materials.
Fan, et al., (xe2x80x9cDesign of Three-Dimensional Photonic Crystals at Submicron Lengthscalesxe2x80x9d, Appl. Phys. Lett., 65, 11, Sep. 12, 1994) describe a class of periodic, three-dimensional dielectric photonic crystal structures amenable to submicron-scale fabrication. Fabrication involves creating a layered structure of materials alternating in dielectric constant, and etching (drilling) holes through the article normal to the layered structure. Specifically, the layered structure is created by depositing a layer of silicon on a substrate, etching grooves into the resulting silicon layer, and filling the grooves with silicon dioxide. Another layer of silicon is deposited on the first layer, grooves offset from those of the first set of grooves are etched, and those grooves filled with silicon dioxide. The process is repeated to create the multi-layered structure, through which the holes are etched. Assuming dielectric constants of 12.096 for silicon and 2.084 for silicon dioxide, (both at wavelength=1.53 microns), the band gap was computed to extend from wavelength=1.43 microns to 1.64 microns.
Joannopoulos, et al. (referenced above) provides an overview of photonic band gap materials, and their theoretical treatment. Experimental results are reported, including construction of a two-dimensional crystal lattice that reflects essentially all in-plane light within a specified frequency band. Specifically, construction involved etching a triangular lattice of air columns in a crystal via electron-beam lithography (see Wendt, et al., xe2x80x9cNanofabrication of Photonic Lattice Structures in GaAs/AlGaAsxe2x80x9d, J. Vac. Sci. and Tech. B. 11, 2637 (1993)). The columns of air were fabricated having a radius of 122.5 nm, the lattice constant was 295 nm, and the columns were about 600 nm tall.
International Patent Application WO 97/01440 to 3M, entitled xe2x80x9cMultilayer Polymer Film with Additional Coatings or Layersxe2x80x9d (""440) describes a multilayer polymeric film including a plurality of alternating polymer layers that may act as a mirror or polarizer. The multilayer polymer films described in ""440 include alternating layers of at least two materials where at least one of the materials has the property of stress induced birefringence, such that the index of refraction of the material is affected by mechanical stretching. By stretching the multilayer stack either uniaxially or biaxially, an optical film may be created with a range of reflectivities for differently oriented plain-polarized incident light. Desired refractive index contrast can be obtained by stretching the polymer films during or after film formation.
Chen, et al., xe2x80x9cTheoretical Prediction of the Optical Waveguiding Properties of Self-Assembled Block Copolymer Filmsxe2x80x9d, Macromolecules, 17, (1995) describe a lamellar-forming block copolymeric waveguide, and computer calculations of propagation constants and optical field intensity distributions of selected diblock and triblock copolymeric thin-film waveguides. It is reported that by choosing the chemical composition of each block, the refractive index of each layer can be precisely controlled. Where the refractive index of a guiding layer is greater than the refractive indices of the substrate and superstrate layers, a waveguide can result. Chen, et al. report that the domain size of individual lamellae can be varied from tens of angstroms to thousands of angstroms.
U.S. Pat. No. 5,281,370 (""370) to Asher et al. entitled xe2x80x9cMethod of Making Solid Crystalline Narrow Band Radiation Filterxe2x80x9d describes a method for making a solid polymeric optical filter material which filters a predetermined wavelength band from a broader spectrum of radiation. The method includes creating a colloidal suspension composed of polymeric particles dispersed within a medium, arranging the particles, for example by electrophoresis, to form an ordered array, and fixing the structure, for example by fusing the particles together, to yield a solid three-dimensional array having a periodic lattice spacing.
Three-dimensional periodicity in block-copolymeric, self-assembled structures are known. (Thomas, et al., xe2x80x9cPhase Morphology in Block Copolymer Systemsxe2x80x9d, Phil. Trans. R. Soc. Lond. A., 348, 149-166). Lamellar, cylindrical, spherical, and ordered bicontinuous double diamond morphologies in block copolymeric systems have been identified (see, for example, Helfand, et al., Developments in Block Copolymers. 1; Goodman, I., Ed.; Applied Science Publishers: London, 1982; vol. 1, pp. 99-126; Herman, et al., Macromolecules, 20, 2940-2942, (1987). Researchers have been successful in incorporation of metallic species, including clusters, selectively in a first but not a second domain of a two-domain species resulting from thermodynamic phase separation of block copolymeric species Sankaran, et al., xe2x80x9cSynthesis of Zinc Sulfide Clusters and Zinc Particles Within Microphase-Separated Domains of Organometallic Block Copolymersxe2x80x9d, Chem. Mater., 5, 1133-1142 (1993); Sohn, et al., xe2x80x9cProcessable Optically Transparent Block Copolymer Films Containing Superparamagnetic Iron Oxide Nanoclustersxe2x80x9d, Chem. Mater., 9, 1, 264-269 (1997). Sankaran, et al. and Sohn, et al. pursued goals of creating monodisperse metal/semiconductor clusters in an organized array for the purpose of growing metal clusters in a controlled fashion for electrical, optical, magnetic, and catalytic applications. These and other techniques have shown some promise with respect to several diverse goals. However, there is a need in the art for inexpensive, simple, photonic band gap materials, and it is an object of the present invention to provide such materials.
The present invention provides a series of systems, polymeric materials, and methods associated with photonic band gap materials. The methods include methods of forming such materials and methods of use of such materials, and can be used in conjunction with any of the systems or polymeric materials of the invention. That is, all of the systems described below can be made using the methods of making materials described, and can be used in the methods of using photonic band gap materials. The methods of manufacture and use of photonic band gap materials described herein can be applied to all of the systems or polymeric materials described herein.
In one aspect, the invention provides a series of systems. One system includes a polymeric article having a periodic structure of a plurality of periodically occurring separate domains. The domains include at least a first and a second domain that each have a characteristic dimension from about 50 nm to about 1500 nm. The article has a refractive index ratio of at least about 1.1 for a continuous set of wavelengths lying within a range from about 100 nm to about 10 microns. That is, the article has a refractive index ratio of at least about 1.1 for at least one wavelength domain or continuous plurality of wavelengths, lying within a range of from about 100 nm to about 10 microns.
In another embodiment, a similar system is provided. In this embodiment, the first and the second domains each have a characteristic dimension from about 15 nm to about 50 nm and a refractive index ratio of at least about 1.2 for a continuous set of wavelengths lying within a range from about 50 nm to about 1000 nm.
In another embodiment, a similar system is provided that has a characteristic dimension of from about 300 nm to about 5000 nm and a refractive index ratio of greater than 1.0. The refractive index ratio is for a continuous set of wavelengths lying within a range from about 400 nm to about 50 microns.
In another embodiment, a system is provided that includes a structurally periodic polymeric structure including a defect in periodicity. The defect is at least partially transparent to electromagnetic radiation in a wavelength range of from about 100 nm to about 50 microns. A portion surrounds the defect which is reflective to the electromagnetic radiation.
In another embodiment, a system is provided that comprises a polymeric article including a three-dimensional periodic variation in refractive index.
In another aspect, the invention provides a series of methods. One method involves exposing a portion of a polymeric article in an ordered state, having a pathlength to electromagnetic radiation within a free space wavelength range of from about 50 nm to about 50 microns. The article is allowed to inhibit transmittance of the electromagnetic radiation to an extent greater than the article would inhibit that transmittance in a disordered state, at the frequency through the pathlength.
Another method of the invention involves creating a defect in a polymeric article including a periodic structure of a plurality occurring separate domains. The defect can be created by inserting into the material a plane of a material different from materials defining the polymeric article.
According to another method of the invention, a defect is created in a polymeric article, including a periodic structure of a plurality of periodically occurring separate domains, by altering polymeric material in the article. The polymeric material can be altered by removing polymeric material via radiation, by exposing the material to intersecting beams of radiation, by removing the material via etching or the like. A defect can be created in one embodiment by magnetically guiding a heated object through the article.
The systems or method of the invention can include at least one auxiliary refractive modifier in at least one of the first and the second domains. The refractive index modifier can be particulate material, a dye, a polymeric particulate material, a ceramic, semi-conductor, or other particulate material, or the like, and can provide a refractive index ratio in the article of greater than 1, or at least about 1.1, 1.2, 1.3, 1.4, 1.5, 2.0, or 4.0, in other embodiments.
The systems and methods of the invention can involve a polymeric article that has a one-dimensional structure, a two-dimensional periodic structure, or a three-dimensional periodic structure, and can be formed from polymeric materials that are self-assembled from self-assembly of polymeric materials to form separate domains followed by removal of one domain and replacement with a additive material such as a non-polymeric material. That is, first and second domains can be formed by polymeric self-assembly of the first domain and a polymeric precursor of the second domain, followed by replacement of the precursor by a non-polymeric material.
The systems and methods of the invention can involve a polymeric article that includes a block co-polymer having at least two Blocks A and B that are assembled into the first and second domains, respectively. The polymeric article can also include at least three blocks, A, B and C wherein the blocks A and B are self-assembled into the first and the second domains.
The systems and methods of the invention can include polymeric articles that include at least one defect in periodicity. The defect in periodicity can be a point, line, planer defect, or combination thereof, and the defect can have a width, length and height. Where the polymeric article is at least two-dimensionally periodic, the defect can be provided in at least one of the two dimensions, or in two dimensions. Where the polymeric article is three-dimensional periodic, the defect can be provided in one, two or three dimensions. The defect can be a series of interconnected points, or a line having a width and a length at least five times the width, and other geometric arrangements. A defect can be a continues pathway that is non-linear, and can be three-dimensionally non-linear. The defect can be in the order of dielectric domains of the structure and can be a defect in refractive index between at least two adjacent domains of a polymeric article.
In some embodiments, the polymeric article of systems or methods of the invention can include a metallic species, rather than a refractive index-modifying species. The metallic species can be a refractive index-modifying species, or another metallic species residing primarily in one domain, selectively.
Systems or methods of the invention can include polymeric articles that are periodic arranged structures of a plurality of separate domains. The structure can inhibit transmittance of electromagnetic radiation at a free-space wavelength range from about 50 nm to about 50 microns relative to transmission of electromagnetic radiation at the wavelength through a system comprised of the same materials, but in a disarranged state. These structures can inhibit transmittance at a free-space wavelength range of from about 300 nm to about 50 microns in other embodiments. A periodic arranged structure can be provided in accordance with systems or methods of the invention that has a photonic band gap in at least one direction within a free-space wavelength range of from about 50 nm to about 50 microns. A periodic arranged structure can have a photonic band gap in at least one direction within a free-space wavelength range of from about 300 nm to about 50 microns.
Systems or methods of the invention can include polymeric articles that in a disarranged state, are at least partially transparent to light within a wavelength range of from about 100 nm to about 10 microns, or a wavelength range of from about 400 nm to about 50 microns.
The invention also provides systems that are block copolymers. One block copolymeric species has at least two blocks A and B. The blocks A and B are incompatible with each other such that the block copolymer species is self-assembleable into a periodic structure of a plurality of at least first and second, separate domains, each defined by association of similar blocks of the copolymer species. The periodic structure into which the block copolymer species is self-assembleable is able to contain at least one auxiliary index of refraction enhancing additives such that the first and second domains have a refractive index ratio of at least 1.1 at a wavelength of from about 100 nm to about 10 microns, or other refractive index ratios for a continuous set of wavelengths lying within ranges as described herein. In one embodiment, the molecular weight of the block copolymeric species is at least 80,000 Daltons. In another embodiment, the molecular weight is at least 500,000 Daltons, and in another embodiment, at least 2,000,000 Daltons.
Another method of the invention involves a method for processing a block copolymer. In one embodiment, a block copolymer is processed to produce a phase-separated polymeric multi-domain structure. The structure includes a periodic variation in refractive index of a dimension on the order of from about 100 nm to about 50 microns, to the extent that the article defines a photonic band gap structure. The block co-polymer can be allowed to self-assemble into the phase-separated polymeric multi-domain structure and this can occur in the presence of an applied, electric, magnetic, or mechanical flow field in certain embodiments. In one preferred embodiment, the phase-separated structure is self-assembled in the presence of an applied electromagnetic field.
Systems of the invention can include a metallic coating on metallic particles that reside primarily in one domain selectively.
Other advantages, novel features, and objects of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings, which are schematic and which are not intended to be drawn to scale. In the figures, an identical or nearly identical component that is illustrated in various figures, is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.